Stock-Based Compensation Plans - Nonqualified Stock Options, Activity (Details) - Nonqualified Stock Options - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in options outstanding
Options outstanding at beginning of period (in shares)	7.5
Options granted (in shares)	0.7
Options exercised (in shares)	2.9
Options expired (in shares)	1.0
Options outstanding at end of period (in shares)	4.3	7.5
Options vested or expected to vest at end of period (in shares)	4.3
Options exercisable at end of period (in shares)	2.7
Options outstanding at beginning of period, Weighted-average exercise price (in dollars per share)	$ 44.61
Options granted, Weighted-average exercise price (in dollars per share)	62.78
Options exercised, Weighted-average exercise price (in dollars per share)	46.07
Options expired, Weighted-average exercise price (in dollars per share)	62.59
Options outstanding at end of period, Weighted-average exercise price (in dollars per share)	42.65	$ 44.61
Options vested or expected to vest at end of period, Weighted-average exercise price (in dollars per share)	42.62
Options exercisable at end of period, Weighted-average exercise price (in dollars per share)	$ 38.74
Options outstanding at end of period, Intrinsic value	$ 120.3
Options vested or expected to vest at end of period, Intrinsic value	120.1
Options exercisable at end of period, Intrinsic value	88.1
Total intrinsic value of options exercised	$ 53.0	$ 25.7	$ 17.4
2014 Stock Incentive Plan, Amended and Restated 2010 Stock Incentive Plan and Stock Incentive Plan
Stock-Based Compensation Plans - Disclosures
Option expiration period	10 years
Vesting period	3 years
Change in options outstanding
Options granted (in shares)	0.7	1.1	0.6